Within the framework of driver assistance systems, radar sensors are increasingly being used in motor vehicles for sensing the traffic environment, for example, for radar-based distance control (adaptive cruise control systems/ACC). Such a cruise control system is described, for example, in “Adaptive Fahrgeschwindigkeitsregelung ACC,” (Adaptive Cruise Control ACC) yellow technical instruction series, 2002 edition by Robert Bosch GmbH.
Due to the flat design and ease of manufacture thereof, for example in etching processes, what are generally referred to as planar antenna devices or patch antennas are particularly suited for use in the above described radar sensors. In the case of such antennas, it is a question of a two-dimensional array of radiating resonators (antenna elements, respectively patch elements/patches), each having a defined amplitude and phase. By superimposing the radiation diagrams of the individual patch elements, one obtains the resulting radiation diagram of the antenna, the rows being responsible for the azimuthal characteristic and the columns for the elevation characteristic. The antenna elements are usually configured in vertically oriented antenna columns.
Many radar sensors used for driving-environment sensing in automotive applications make use of such planar antenna designs. One advantage of the planar antenna designs is the low overall depth of the radar sensors resulting therefrom. Greater flexibility is thereby attained for the installation location of the radar sensors, and new fields of application emerge, such as installation in the side region of the vehicle. Besides the size of the radar sensors, the costs of manufacturing the same are naturally also a determining factor. Especially in planar antenna designs, where a signal evaluation is performed on the individual channels (no HF beam-forming), the number of mixers used constitutes a considerable cost factor. In this context, the configuration, respectively the number of antenna patches plays an important role. Conventional radar sensors having planar antenna devices generally have a uniform linear array (ULA) structure. The antenna columns having the patch elements are spaced at equidistant intervals which generally reside within the range of half of the wavelength in air (λ/2).
The antenna aperture is the decisive factor in achieving a best possible angular precision using the radar sensor system. The larger the antenna aperture is, the better is the angular precision. If the antenna aperture is provided with a uniform linear array structure, as in previously known radar sensors, a large number of mixers is then required, thereby increasing the total costs for the sensors.
German Patent Application No. DE 100 36 131 A1 describes a radar sensor used for sensing the traffic situation in the driving environment of a motor vehicle. It includes a carrier element having an array of patch antennas in the form of a combination of a filled subarray of patch antennas and a sparse subarray of patch antennas. However, the patch antennas are provided redundantly, i.e., the signal relations are measured multiple times.